4.2-25*0.7÷5
=4.2-5*0.7
=4.2-3.5
=0.7
4.7*2.34-0.34*4.7
=4.7*（2.34-0.34）
=4.7*2
=9.4
28.7*[0.54÷（8.7+45.3）]
=28.7*[0.54÷54]
=28.7*0.01
=0.287